Asymmetric Diels–Alder reactions between chiral sugar nitroalkenes and 1-O-substituted buta-1,3-dienes. Synthesis and reactivity of new cyclohexenyl derivatives

New C-aryl alditols from Diels-Alder adducts of sugar nitroalkenes

“…19,20 Determination of structures of nitrobenzene pentitol peracetates 6a and 6b is based on their analytical and spectroscopic data. The 1 H and 13 C NMR spectra of both compounds show four protons and six carbon atoms in the aromatic region; the values of the vicinal proton coupling constants in the sugar side-chain are similar to those of their starting materials, 15 thus supporting the same extended conformation in the acyclic carbohydrate moiety. Treatment of 6a and 6b with potassium carbonate in 90% methanol yielded the deacetylated derivatives 6c and 6d, respectively.…”

“…By comparison with closely related reactions, the milder conditions now used for these processes are noticeable: Treatment of 2a or 4b with sodium acetate in boiling THF only induced anti-elimination of acetic acid, yielding nitrocyclohexadienes; 15 under these conditions, stereoisomers of 2a and 4b did not undergo the desired syn-elimination, probably because of the unfavorable conformation that has to be adopted by the cyclohexene ring.…”

“…On the other hand, 3-glyco-2-nitrophenols 16a and 16b were prepared from crude hydrolysis mixtures 15 of the corresponding cycloadducts 12-15 by treatment with dimethylsulfoxide and acetic anhydride. As described previously, 29 these reagents oxidize primary or secondary alcohols to carbonyl compounds, whereas in our case the oxidation led to nitrophenols 16a and 16b, probably through the enol form of the initially formed cyclohexenone.…”

“…Based on our previous experience with Diels-Alder reactions of sugar derivatives, [13][14][15] we report herein the synthesis of several C-aryl alditols. Cycloadducts obtained from D-galacto-and D-manno-3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitrohept-1,2-enitols 1a, 16 1b 17 ( Figure 1) with furan, 1-acetoxy-, or 1-trimethylsilyloxybuta-1,3-dienes were used as starting materials.…”

1-Acetoxy-1,3-butadiene

“…[4 + 2] Cycloadditions between sugar substituted chiral trans-nitroalkenes and 1acetoxyl-1,3-butadiene led to new nitro-substituted cyclohexenyl derivatives (eq 15). 40 It is noteworthy that when employing tetraacetyl D-galactose-based-auxiliary, a sole product was formed.…”